Luiz Henrique de P. Melo

Influences of Duration of Inspiratory Effort, Respiratory Mechanics, and Ventilator Type on Asynchrony With Pressure Support and Proportional Assist Ventilation

BACKGROUND: Pressure support ventilation (PSV) is often associated with patient-ventilator asynchrony. Proportional assist ventilation (PAV) offers inspiratory assistance proportional to patient effort, minimizing patient-ventilator asynchrony. The objective of this study was to evaluate the influence of respiratory mechanics and patient effort on patient-ventilator asynchrony during PSV and PAV plus (PAV+). METHODS: We used a mechanical lung simulator and studied 3 respiratory mechanics profiles (normal, obstructive, and restrictive), with variations in the duration of inspiratory effort: 0.5, 1.0, 1.5, and 2.0 s. The Auto-Trak system was studied in ventilators when available. Outcome measures included inspiratory trigger delay, expiratory trigger asynchrony, and tidal volume (VT). RESULTS: Inspiratory trigger delay was greater in the obstructive respiratory mechanics profile and greatest with a effort of 2.0 s (160 ms); cycling asynchrony, particularly delayed cycling, was common in the obstructive profile, whereas the restrictive profile was associated with premature cycling. In comparison with PSV, PAV+ improved patient-ventilator synchrony, with a shorter triggering delay (28 ms vs 116 ms) and no cycling asynchrony in the restrictive profile. VT was lower with PAV+ than with PSV (630 mL vs 837 mL), as it was with the single-limb circuit ventilator (570 mL vs 837 mL). PAV+ mode was associated with longer cycling delays than were the other ventilation modes, especially for the obstructive profile and higher effort values. Auto-Trak eliminated automatic triggering. CONCLUSIONS: Mechanical ventilation asynchrony was influenced by effort, respiratory mechanics, ventilator type, and ventilation mode. In PSV mode, delayed cycling was associated with shorter effort in obstructive respiratory mechanics profiles, whereas premature cycling was more common with longer effort and a restrictive profile. PAV+ prevented premature cycling but not delayed cycling, especially in obstructive respiratory mechanics profiles, and it was associated with a lower VT.

Influence of the ventilatory mode on acute adverse effects and facial thermography after noninvasive ventilation

To compare the incidence and intensity of acute adverse effects and the variation in the temperature of facial skin by thermography after the use of noninvasive ventilation (NIV).We included 20 healthy volunteers receiving NIV via oronasal mask for 1 h. The volunteers were randomly divided into two groups according to the ventilatory mode: bilevel positive airway pressure (BiPAP) or continuous positive airway pressure (CPAP). Facial thermography was performed in order to determine the temperature of the face where it was in contact with the mask and of the nasal dorsum at various time points. After removal of the mask, the volunteers completed a questionnaire about adverse effects of NIV.The incidence and intensity of acute adverse effects were higher in the individuals receiving BiPAP than in those receiving CPAP (16.1% vs. 5.6%). Thermographic analysis showed a significant cooling of the facial skin in the two regions of interest immediately after removal of the mask. The more intense acute adverse effects occurred predominantly among the participants in whom the decrease in the mean temperature of the nasal dorsum was lower (14.4% vs. 7.2%). The thermographic visual analysis of the zones of cooling and heating on the face identified areas of hypoperfusion or reactive hyperemia.The use of BiPAP mode was associated with a higher incidence and intensity of NIV-related acute adverse effects. There was an association between acute adverse effects and less cooling of the nasal dorsum immediately after removal of the mask. Cutaneous thermography can be an additional tool to detect adverse effects that the use of NIV has on facial skin.Comparar a incidencia e a intensidade de efeitos adversos agudos e a variacao da temperatura da pele da face atraves da termografia apos a aplicacao de ventilacao nao invasiva (VNI).Foram incluidos 20 voluntarios sadios, de ambos os generos, submetidos a VNI com mascara oronasal por 1 h e divididos aleatoriamente em dois grupos de acordo com o modo ventilatorio: bilevel positive airway pressure (BiPAP) ou continuous positive airway pressure (CPAP). A termografia da face foi realizada para determinar a temperatura na regiao de contato da mascara e no dorso do nariz em momentos diferentes. Os voluntarios preencheram um questionario de efeitos adversos apos a retirada da VNI.A incidencia e a intensidade dos efeitos adversos agudos foram maiores naqueles submetidos a BiPAP em relacao aos submetidos a CPAP (16,1% vs. 5,6%). A analise termografica evidenciou um esfriamento significativo da pele facial nas duas regioes de estudo imediatamente apos a retirada da mascara. Os efeitos adversos agudos em maior intensidade ocorreram predominantemente no grupo de participantes cuja reducao da temperatura media no dorso do nariz foi menor (14,4% vs. 7,2%). A analise visual termografica de zonas de esfriamento e aquecimento na face identificou regioes de hipoperfusao ou hiperemia reativa.O uso do modo BiPAP associou-se a maior incidencia e intensidade de efeitos adversos agudos associados a VNI. Houve associacao entre efeitos adversos agudos e menor esfriamento da pele do dorso do nariz imediatamente apos a retirada da mascara. A termografia cutânea pode ser uma ferramenta adicional na deteccao de efeitos adversos na pele da face associados ao uso da VNI.